1. Field of the Invention
The present invention relates to a drive transmission system equipped with a stationary shaft member secured to an apparatus body and a drive transmission gear rotatable around the stationary shaft member, and in particular to a driving system and an image forming apparatus each equipped with the drive transmission system.
2. Description of the Background Art
In accordance with a demand for a longer-lasting, more durable image forming apparatus that employs an electro-photographic system, a drive transmission system that transmits a rotation driving force from a driving source to a rotation member such as a photo-conductive member is also required to be long-lasting and durable. In one such known exemplary drive transmission system, a stationary shaft member is secured to a casing of an apparatus body while a drive transmission gear rotates around the stationary shaft member to transmit a rotation driving force from a driving source to a rotation member via a drive transmission gear. In such a drive transmission system, in order for the drive transmission system can enjoy a longer life, durability of in order for the drive transmission system can enjoy a longer life, durability of a rotational sliding section existing between the drive transmission gear and the stationary shaft member must be improved.
As a system that improves such durability of the rotational sliding section, a coupling drive mechanism serving as a drive transmission system is employed as described in Japanese Patent Application Laid Open No. 2001-82474 (JP-2001-82474-A). Specifically, a bearing member is provided in a rotational sliding section between a drive transmission gear and a stationary shaft member. However, the bearing member is rarely employed in the rotational sliding section in compact, inexpensive image forming apparatuses.
Further, in a drive transmission system excluding such a bearing member in the rotational sliding section, an inner circumferential surface of the drive transmission gear generally slides while in frictional contact with an outer circumferential surface of the stationary shaft member when the drive transmission gear is rotated. Accordingly, the sliding section of the inner circumferential surface of the drive transmission gear (hereinafter referred to as a gear inner circumference sliding section) and that of the outer circumferential surface of the sliding section of the stationary shaft member (hereinafter referred to as a shaft outer circumferential sliding section) need improved durability.
Further, it is known that one image forming apparatus in actual use employs a drive transmission system in which a grease groove filled with grease is provided on an outer circumferential surface of the stationary shaft member.
For example, some conventional drive transmission systems include grease grooves on outer circumferential surfaces of stationary shaft members as shown in FIGS. 11 and 12, respectively, wherein FIG. 11A illustrates a section when viewed along a line B-B of FIG. 11B, through which a rotation central line of a drive transmission system passes, and FIG. 11B illustrates a front view of the drive transmission system in a direction shown by an arrow A of FIG. 11A, respectively. In a first conventional drive transmission system 200, there are provided a stationary shaft member 61 secured to a frame 75 serving as a casing of an apparatus body and a drive transmission gear 64 rotating around the stationary shaft member 61. As shown, an input gear for inputting a driving force to the drive transmission gear 64 and an output gear for outputting a driving force from the drive transmission gear 64 are also provided but omitted from FIGS. 11A and 11B.
In such a first conventional drive transmission system 200, when a driving force is transmitted from an input gear, not shown, to the drive transmission gear 64, the drive transmission gear 64 rotates in a direction shown by an arrow C. At that moment, a gear inner circumferential surface 64f of the drive transmission gear 64 slides on a shaft outer circumferential surface 61f of the stationary shaft member 61. Further, a grease groove 62 filled with the grease 63 is provided on the shaft outer circumferential surface 61f in a shaft direction of the stationary shaft member 61. When the drive transmission gear 64 rotates in a direction shown by an arrow C, a portion of the gear inner circumferential surface 64f to which the grease is attracted moves to a position facing the shaft outer circumferential surface 61f. As a result, the grease 63 can enter a section between the gear inner circumference sliding section of the gear inner circumferential surface 64f and the shaft outer circumference of the shaft outer circumferential surface 61f, thereby suppressing wear and improving durability of the gear inner circumference sliding section and the shaft outer circumferential surface sliding section.
However, in such a first conventional drive transmission system 200, the shaft direction in which the groove edge section 61e extends as a boundary between the shaft outer circumferential surface 61f and the grease groove 62, and the direction in which the gear inner circumferential surface 64f moves in relation to the stationary shaft member 61 are orthogonal to each other. In such a situation, when the drive transmission gear 64 rotates, the groove edge section 61e contacts the gear inner circumferential surface 64f sliding around the stationary shaft member 61 in a counter direction, so that the gear inner circumferential surface 64f slides in friction with the groove edge section 61e, and is susceptible to burn-out.
A second conventional drive transmission system is then utilized to resolve such a problem, as described with reference to FIG. 12, which illustrates a cross section of a drive transmission gear 64 along its rotation central line 64a. 
Specifically, in the second conventional drive transmission system 200, there are provided a stationary shaft member 61 secured to a frame 75 serving as a casing of an apparatus body and a drive transmission gear 64 rotating around the stationary shaft member 61. Further provided are an input gear 65 for inputting a driving force from a drive motor 500 to a drive transmission gear 64 and an output gear 69 for outputting a driving force from the drive transmission gear 64 to a driven section, not shown. The drive transmission gear 64 is a two-step gear having large- and small-diameter sections 77 and 79, respectively. When the drive motor 500 operates and accordingly the input gear 65 rotates, a rotational driving force caused in this way is inputted to the large diameter section 77, thereby rotating the drive transmission gear 64. Owing to the rotation of the drive transmission gear 64, the small diameter section 79 of the drive transmission gear 64 and the output gear 69 linked therewith rotate, so that a rotation driving force of the drive motor 500 is transmitted to the driven section.
The large diameter section 77 of the drive transmission gear 64 and the input gear 65 employ helical gears, respectively. Thus, a thrusting force acts on the drive transmission gear 64 in a direction shown by arrow D in parallel to a rotation central line 64a when the input gear 65 and the drive transmission gear 64 rotate. Consequently, when the drive motor 500 operates and a rotation driving force caused in this way is inputted to the drive transmission gear 64, the drive transmission gear 64 moves in a direction in which a thrusting force acts by an amount of thrusting allowance 68 and rotates there colliding with a washer 74.
When the drive motor 500 stops, the drive transmission gear 64 is biased by a biasing member in a direction opposite to the thrusting force acting direction, and separates from the washer by the amount of thrusting allowance 68. By repeating such controlling of the drive motor 500, the drive transmission gear 64 moves reciprocally in the thrusting direction of the shaft line direction. Further, a grease groove 62 filled with grease 63 is provided entirely around a shaft outer circumferential surface 61f of a cylindrical stationary shaft member 61. When the driving motor 500 operates thereby moving the drive transmission gear 64 in the thrusting direction, a portion of the gear inner circumferential surface 64f facing the grease groove 62 while receiving the grease 63 therefrom while the motor is stopped is shifted to a different position facing the shaft outer circumferential surface 61f on a thrusting direction side of the grease groove 621. Thus, the grease 63 is attracted to the different position on the shaft outer circumferential surface 61f. Subsequently, when the driving motor 500 stops and the drive transmission gear 64 moves in the opposite direction to the thrusting direction, the grease attraction portion on the shaft outer circumferential surface 61f faces the shaft outer circumferential surface 61f on a thrusting direction side than that facing the grease groove 62 during the stop condition. Thus, the grease 63 can be attracted to the portion on the gear inner circumferential surface 64f. By repeating such controlling of the drive motor 500 and reciprocating the drive transmission gear 64 along the shaft line direction in this way, the grease in the grease groove 62 can be supplied in the thrusting direction. Thus, the grease 63 can enter between the gear inner circumferential surface 64f and the shaft outer circumferential surface 61f. As a result, wear is suppressed in the gear inner circumference sliding section and the shaft outer circumference sliding section, so that durability can be improved.
Further, since the groove edge section 61e serving as a boundary between the grease groove 62 and the shaft outer circumferential surface 61f is arranged in a sliding direction, the grease groove 62 and the shaft outer circumferential surface 61f do not slide in friction with each other, and burning does not occur therebetween when the drive transmission gear 64 rotates.
However, since an inner diameter of a portion of a gear inner circumferential surface 64f facing a shaft outer circumferential surface 61f and that of a portion of a gear inner circumferential surface 64f facing a grease groove 62 are substantially the same, only an amount of grease equivalent to a capacity of the grease groove 62 can be filled in the grease groove 62 and cannot be continuously supplied for a long time period between the gear inner circumferential surface 64f and the shaft outer circumferential surface Elf.
Further, when the grease is insufficiently supplied between the gear inner circumferential surface 64f and the shaft outer circumferential surface 61f, sliding load increases therebetween, and accordingly a life of the drive transmission system becomes short.